P079D code meaning
Transmission Friction Element D Slip Detected
Powertrain system Generic code P07xx codes Check engine light
What P079D means
The 'friction element slip' codes monitor a clutch that is commanded locked in a power-split hybrid transmission: the module calculates its slip from electric motor, engine and output speeds (target 0 rpm) and flags slip above a threshold for a minimum time, with sufficient line pressure and clutch torque; from 2016 GM also flags a calculated friction energy threshold at once. The letter matches the manufacturer's clutch number. P079D concerns clutch 4 and is used only by GM's Two-Mode SUVs and pickups (2008–13) with four clutches: slip above 100 rpm for 0.3 s at commanded pressure of at least 1800 kPa and 20 Nm torque, after two trips. Volt, Malibu Hybrid and CT6 do not use it.
P079D at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 12 hours
- Clears after repairAfter a drive cycle
Symptoms of P079D
- Check engine light or 'service hybrid system' message
- Limp mode with reduced power or restricted drive mode
- Slipping, engine speed rises without drive
- Jolt when the engine starts or stops
Common causes of P079D
- Most likelyClutch D plates worn or glazed
- PossibleToo little line pressure: low or aged fluid, filter, auxiliary oil pump or blocked pressure orifice
- PossiblePressure or shift valve of clutch D or valve body sticking
- Less likelyModule software (false setting)
- Less likelyFaulty speed signals (motor resolver, output)
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Transmission clutchesTransmission valve bodyAuxiliary transmission oil pumpHybrid control module
What each part of P079D means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 7 | Area: transmission. |
| 9D | The exact fault in that area. |
What to do next
- Note P079D and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P079D
What does P079D mean?
P079D means "Transmission Friction Element D Slip Detected". The 'friction element slip' codes monitor a clutch that is commanded locked in a power-split hybrid transmission: the module calculates its slip from electric motor, engine and output speeds (target 0 rpm) and flags slip above a threshold for a minimum time, with sufficient line pressure and clutch torque; from 2016 GM also flags a calculated friction energy threshold at once. It is a generic code, so it means the same on every make.
Is it safe to drive with P079D?
Drive gently and only to a workshop. With P079D the car can go into limp mode (reduced power) to protect itself.
Will P079D fail an emissions test?
Yes, it can. P079D is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P079D to fix?
Difficulty: hard. A typical repair takes 1 to 12 hours of work. This is a job for a workshop.
Will P079D clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.